phenomena in a system moving with any velocity less than that of light / by H.A. Lorentz -- On the electrodynamics of moving bodies / by A. Einstein -- Does the. physics students we studied the Special Theory of Relativity. Yet Albert Einstein's original paper that started it all, “On the. Electrodynamics of Moving Bodies,”[1]. ELECTRODYNAMICS. OF MOVING BODIES. By A. Einstein. June 30, It is known that Maxwell's electrodynamics--as usually understood.

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By A. EINSTEIN. June 30, It is known that Maxwell's electrodynamics—as usually understood at the present time—when applied to moving bodies, leads. ELECTRODYNAMICS OF MOVING BODIES Doc. ON THE ELECTRODYNAMICS OF MOVING BODIES by. A. Einstein [Annalen der. Physik 17 (). On the Electrodynamics of Moving Bodies ( edition) The Principle of Relativity: Original Papers by A. Einstein and H. Minkowski.

Einstein is often regarded as the father of modern physics and received the Nobel Prize in Physics "for his services to theoretical physics, and especially for his discovery of the law of the photoelectric effect". Einstein published more than scientific papers along with over non-scientific works. His great intelligence and originality have made the word "Einstein" synonymous with genius. Einsteins greatest and most famous theory is the theory of relativity, which fundamentally changed the understanding of physics and astronomy during the 20th century. When first published, relativity superseded a year-old theory of mechanics put forth by Isaac Newton. The theory of relativity overturned the concept of motion from Newton's day, into all motion is relative.

It does not have any references to any other publications. Many of the ideas had already been published by others, as detailed in history of special relativity and relativity priority dispute. However, Einstein's paper introduces a theory of time, distance, mass, and energy that was consistent with electromagnetism , but omitted the force of gravity.

At the time, it was known that Maxwell's equations, when applied to moving bodies, led to asymmetries moving magnet and conductor problem , and that it had not been possible to discover any motion of the Earth relative to the 'light medium' i.

Einstein puts forward two postulates to explain these observations. First, he applies the principle of relativity , which states that the laws of physics remain the same for any non-accelerating frame of reference called an inertial reference frame , to the laws of electrodynamics and optics as well as mechanics. In the second postulate, Einstein proposes that the speed of light has the same value in all frames of reference, independent of the state of motion of the emitting body.

Special relativity is thus consistent with the result of the Michelson—Morley experiment , which had not detected a medium of conductance or aether for light waves unlike other known waves that require a medium such as water or air. Einstein may not have known about that experiment, but states, Examples of this sort , together with the unsuccessful attempts to discover any motion of the earth relatively to the " light medium ", suggest that the phenomena of electrodynamics as well as of mechanics possess no properties corresponding to the idea of absolute rest.

The speed of light is fixed, and thus not relative to the movement of the observer. This was impossible under Newtonian classical mechanics.

Einstein argues, the same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good. We will raise this conjecture the purport of which will hereafter be called the "Principle of Relativity" to the status of a postulate , and also introduce another postulate, which is only apparently irreconcilable with the former, namely, that light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body.

These two postulates suffice for the attainment of a simple and consistent theory of the electrodynamics of moving bodies based on Maxwell's theory for stationary bodies.

The introduction of a " luminiferous ether " will prove to be superfluous in as much as the view here to be developed will not require an "absolutely stationary space" provided with special properties, nor assign a velocity-vector to a point of the empty space in which electromagnetic processes take place.

The theory […] is based—like all electrodynamics—on the kinematics of the rigid body , since the assertions of any such theory have to do with the relationships between rigid bodies systems of co-ordinates , clocks , and electromagnetic processes. Insufficient consideration of this circumstance lies at the root of the difficulties which the electrodynamics of moving bodies at present encounters.

It had previously been proposed, by George FitzGerald in and by Lorentz in , independently of each other, that the Michelson—Morley result could be accounted for if moving bodies were contracted in the direction of their motion.

His explanation arises from two axioms. First, Galileo's idea that the laws of nature should be the same for all observers that move with constant speed relative to each other. Einstein writes, The laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or the other of two systems of co-ordinates in uniform translatory motion.

The second is the rule that the speed of light is the same for every observer. Any ray of light moves in the "stationary" system of co-ordinates with the determined velocity c, whether the ray be emitted by a stationary or by a moving body.

The theory, now called the special theory of relativity , distinguishes it from his later general theory of relativity , which considers all observers to be equivalent. Special relativity gained widespread acceptance remarkably quickly, confirming Einstein's comment that it had been "ripe for discovery" in Acknowledging the role of Max Planck in the early dissemination of his ideas, Einstein wrote in "The attention that this theory so quickly received from colleagues is surely to be ascribed in large part to the resoluteness and warmth with which he [Planck] intervened for this theory".

In addition, the improved mathematical formulation of the theory by Hermann Minkowski in was influential in gaining acceptance for the theory. Do they hit the ends of the train simultaneously or not? It is the motion of the observer, which determines the answer. For stationary observers on the platform of a station, the events are simultaneous.

For observers on the train they do not hit the opposite ends of the train simultaneously. The reason resides in the finite propagation of light. The train passengers rush toward the light signal from the front and run away from the rear signal. The same is true of the reading of clock times in different reference frames, which move with constant velocity with respect to each other.

The observers will not agree on their respective clock times. Their clocks tick differently, depending on the state of motion.

If there is no cosmic notion of time as Newton assumed , to which all observers can appeal, time must pass at different rates for each observer, depending on the speed of the reference frame. Time cannot be an objective property of the universe. It depends on the perception of observers. By contrast, the physical universe is static, a block universe. Einstein did at times adopt such a philosophy of being. The non-divisibility of the four-dimensional continuum of events does not at all … involve the equivalence of the space co-ordinates with the time co-ordinate.

According to the relational view, time and space are nothing but the order of actual and possible events. Space is the coexistence of such events and time is the order of succession of such coexisting events. In his deliberations of the General theory of relativity, Einstein leaves the reader in no doubt that he regards the total mass-energy distribution in the universe as the source of the space-time metric.

Consider first what would happen, if all references to observers were dropped.

All observers can be replaced by clocks and rods. The clocks in different reference systems will be affected by the respective relative motions of the systems. No observer will conclude that there must be a mysterious transience of time—a moving Now, signalling the march of time from past to future. Without conscious observers, there is no need for the introduction of a tensed view of time, according to which objects change their temporal properties—their dates—by moving from past to present to future.

Events are juxtaposed like beads on a string B-series. The physical world just is, it is a block universe. The passing of time is a human illusion. There is an alternative between these extreme positions of the tensed view versus the block universe.

The tenseless view is mistaken in equating tenselessness with changelessness. Change occurs in the transition between events, even if these events are ordered in four-dimensional Minkowski space-time. Consider, for instance, the famous twin paradox.

One of the two twins is a space traveller who returns to earth after a visit to a distant star only to find that his twin brother, who remained on earth, has aged more than he has. If we were to take the heart beats of the twins as our clocks, these electromagnetic signals, which the twins exchange during the journey, will be subject to the relativistic Doppler Effect with the result that the number of signals the twins receive respectively will not be equal.

A physical change occurs. The relational view already emphasized that time was the order of succession of events.

The crucial notion of the finite propagation of light in STR limits the connectibility of reference frames to time-like connected events.

It is interesting to note that several early commentators on the Special theory already proposed a dynamic interpretations of space-time, according to which worldliness propagate through space-time and acquire a history. But these kinematic relations have entropic aspects, as revealed in the asymmetric behaviour of electromagnetic radiation.

It is these entropic aspects of worldliness, which give the relationist the purchase to consider a dynamic view of spacetime. Einstein considers the question of the temporal direction of events. Imagine we send a signal from B to A through P. This is an irreversible process. On thermodynamic grounds he asserts that a time-like world line from B to A through P in a light cone takes the form of an arrow making B happen before P and A after P see Figure I.

A time-like world line exists between A and B, which lies within, not outside the light cone. But the asymmetrical character of time is here based on a fundamental earlier-later or before-after relation between physical events without reference to an observer.

There is an event, B, at which the signal is emitted. And there is a later event, A, at which the signal is received. This whole event is irreversible. There is an entropy gradient between the state of events at B and A. The assessment of this differential entropy between the two locations does not depend on a particular reference frame. According to a fundamental result of the Special theory of relativity the entropy of a system is frame-independent.

It may be objected that this entropic theory of time could not form the basis for a general dynamic theory of time.

As is well known the second law of thermodynamics is a statistical principle; there is an extremely low probability of a reversal of events in our observable space-time regions.

Although it is unlikely in the life-time of the universe, the second law permits a spontaneous reheating of a glass of cold water by a rearrangement of the molecules. But the arrow of time is supposed to be one-directional. This objection need not worry the relationist in the present context, because the concern here is to establish the possibility of a dynamic interpretation of space-time not on a global but local scale.

Locally, the entropy gradient points in the direction from B to A. All time-like connected observers agree. For the relationist this establishes, within local space-time regions, an order of the succession of events and thereby physical time for time-like related frames.

It points towards a philosophy of becoming since physical time is constituted by the asymmetric, invariant order of physical events in space-time. The existence of the gravitational field is inseparably bound up with the existence of space.

The philosopher must evaluate whether the philosophical consequences, which the physicist claims to follow from the physical discoveries, do indeed follow. This is a question of conceptual evaluation, not empirical testing. We have indicated that a dynamic interpretation of space-time is possible and compatible with the STR.

It is possible if we consider the entropic aspects of space-time events and align the STR to relationist thinking. Quantum Mechanics 13Above we characterized the philosophical consequences of scientific theories—they do not follow deductively but are nevertheless conceptual consequences of these theories.

He thereby uprooted a prior philosophical commitment to absolute time. Scientific revolutions or innovations often upset earlier philosophical presuppositions.

Such presuppositions seem to be unavoidable in science. But in his discussions of quantum mechanics, for example, Einstein was guided by a traditional notion of causality.

In his lifelong opposition to the Copenhagen interpretation of quantum mechanics he disregarded the lesson about thought necessities, which the theory of relativity had taught him. According to Einstein, quantum mechanics was incomplete because it only permitted statistical statements about ensembles of atoms. Quantum mechanics was unable to make precise spatio-temporal predictions about the trajectories of individual atoms.

The ability to make such predictions was for Einstein one of the fundamental requirements of science. Only differential equations, he said, would satisfy the demand of the physicist for causality.

See [Frank ] [Weinert , ch. When Einstein warns that a probabilistic view of quantum mechanics will lead to its incompleteness, on the grounds that it does not allow for precise space-time trajectories of atomic particles, he clings to one of the most venerable presuppositions of classical physics.

In his criticism of Newtonian mechanics, Einstein bemoans the inability to jettison fundamental notions like absolute space and time. But in his view of quantum mechanics he himself relies on a presupposition inherited from classical physics, e. Yet a measurement of the spin property of one particle will instantly change the spin direction of the other particle even over cosmic distances.

The Born interpretation offered him a way out of the dilemma. This incompleteness charge gave him the freedom to believe that a complete description of atomic reality could be found. Einstein yearned for a complete and direct description of reality. Such a complete description of actual events in space-time will avoid non-local effects. The incompleteness charge against QM gave him the freedom to believe that a complete description of reality would recover the differential equations, which described the temporal evolution of real physical systems in space-time.

It was a consequence of a deeper concern with strict causality. Einstein actually maintains that a renunciation of the principle of locality would render empirically testable laws impossible. And locality is expressed in differential equations in real space-time.

See [Einstein ] transl. This principle has been formulated in a number of ways. But locality can also mean that a spin measurement performed on one system, which is spatially separated from another system in the sense of satisfying Einstein locality, cannot influence the spin state of the other system.

His opposition never faltered. Today it is generally regarded as untenable. Quantum systems manifest degrees of entanglement over large distances. Less well-known is that Einstein makes some significant contributions to our understanding of scientific theories. In particular his views harbour a possible solution to the vexing question of the representational power of scientific theories.

The Representational Nature of Scientific Theories 19To Einstein, scientific constructs laws, models, and theories are free inventions of the human mind.

No amount of inductive generalizations can lead from empirical phenomena to the complicated equations of the theory of relativity. But science is not fiction. Science assumes the existence of an external world. Scientific theories are statements about the external world. The kinetic theory of gases models gas molecules as if they were billiard balls. Early atom models modelled atoms as if they were tiny planetary systems.

The role of a principle theory is to propose fundamental principles: the laws of thermodynamics, the principles of relativity, of covariance and invariance, and the constancy of light. These principles constitute constraints on the construction of models and theories. They forbid the occurrence of physical events, like superluminary velocities or perpetual motion machines. Firstly, Einstein was primarily concerned with what he called principle theories, like the theory of relativity.

Here the role of constraints comes to the fore. Einstein often declares the world of experience as the final arbiter of the validity of scientific theories. In Popperian fashion he regarded all scientific theories as falsifiable. But empirical evidence, in the theory of relativity, is only one form of constraint. A scientific theory constructs a coherent and logically rigid account of the available empirical data.

There is nothing final about the representation of a scientific theory of the external world. Theories are free inventions, yet they must retain roots in the empirical world. Does this mean that there is always a plethora of competing theoretical accounts, which nevertheless are compatible with the available evidence? If this were the case scientific theories would face the serious problem of underdetermination. That is, there would always be a number of theories, which are able to explain the empirical evidence, although they fundamentally disagree about their theoretical structure.

For instance the Copernican model of the solar system explains the same observational evidence as the Ptolemaic account although the Copernican model is based on the principle of heliocentrism, while the Ptolemaic account embraces the principle of geocentrism. In this situation Einstein recommends pragmatically to distinguish a logical from a practical point of view. From the logical point of view, Einstein grants that there are always numerous theoretical accounts, which could in principle account for the available evidence.

For there seems to be no limit to the number of competing constructions, which, at least in principle, could claim to give a coherent and simple account of the available phenomena. This is due to the fact that theories are the result of human ingenuity. Yet in practice, the number of available theories is always limited. Einstein did not believe that many competing representations of the empirical world could be sustained.

He goes even further: he believes that there is one correct theory. The structure of the external world has the power to eliminate many rival accounts.

The surviving theory displays such a degree of rigidity that any modification in it will lead to its falsehood. Although we are free to insert any word into the columns and rows of a word puzzle, this freedom is very restricted.

They pose no problem in terms of underdetermination. Rival accounts therefore pose a problem from the point of view of underdetermination. In the practice of science, however, there is little underdetermination. How can this be explained? Einstein locality, logical simplicity and unification are methodological constraints, since they are principles of the methods of science. Compatibility with available and new evidence is an empirical constraint. In the present context the methodological constraints are of lesser importance than some of the other constraints, which are associated with the theory of relativity.

In particular, as we shall see, the light postulate, relativity principles, covariance and invariance principles. We can characterize constraints as restrictive conditions of an empirical or theoretical kind, which descriptive and explanatory accounts must satisfy to count as viable candidates for the scientific description and explanation of the natural world.

With respect to the theory of relativity, Einstein holds that the interplay of specific constraints—like covariance, invariance, relativity—creates a fit of the theory or model with the evidence extracted from the external world. Any modification, he holds, would destroy the coherence of the theory of relativity.

The representation is illustrated in terms of fit, as in the analogy of the crossword puzzle. The structure of the systems is the work of reason; the empirical contents and their mutual relations must find their representation in the conclusions of the theory. In the possibility of such a representation lies the sole value and justification of the whole system, and especially of the concepts and fundamental principles which underlie it. In the simplest case, a model represents the topologic structure of a system; e.

The models used in the theory of relativity are more sophisticated structural models, which combine a topologic with an algebraic structure. The algebraic structure of the model expresses the mathematical relations between the components of the model. This is its topologic aspect. But the main interest lies in the algebraic structure, e.

To carry out the measurements, measuring rods are placed along the radius and tangentially to the edge of the disc. Due to length contraction of the tangential rods the circumference will appear greater on B than on A. Now place two similar clocks on B, one at the centre, C1 and one at the periphery, C2.

Judged from A, C2 will go slower than C1. We may assume that no faulty instruments are involved. These respective measurements are objective. Observers on the respective discs will regard their respective measurements as accurate.

Mathematically, the thought experiment stresses the effect of motion on the measurement of the parameters. Note that the algebraic structure implied by Euclidean geometry fails and must be replaced by a structure provided by Riemannian geometry. The theory of relativity satisfies a number of empirical and theoretical constraints, which improve its fit to the external world.

The empirical facts comprise Einstein famous predictions: the red shift of light as a function of gravitational field strengths and the bending of light rays in the vicinity of strong gravitational fields. He also explains the perihelion advance of Mercury and other planets.

Einstein turned this value into a theoretical postulate such that the speed of light becomes the limit velocity, which no material particle can reach. In the language of the Minkowski representation of space-time this means that from any event, E, light signals converge from the past and diverge into the future at a constant speed, forming past and future cones.

The light cones do not tilt. And all observers measure the same velocity for c, irrespective of the direction and their state of motion with respect to the light source. He complained that according to the then current view an asymmetry of explanation for an observationally indistinguishable phenomenon occurred. If the coil is in motion with respect to the magnet at rest in the ether , the charges in the coil experience a magnetic force, which pushes the electrons around the coil, inducing a current.

If the magnet is in motion with respect to a coil at rest, the magnetic force is no longer the cause of the current, for no magnetic force applies to charges at rest. The magnet now produces an electric field in the coil, resulting in the current. To avoid this asymmetry of explanation—an asymmetry not present in the phenomena—Einstein postulated the physical equivalence of reference frames.

In its general form the principle of relativity states that all coordinate systems, which represent physical systems in uniform or non-uniform motion with respect to each other, must be equivalent from the physical point of view. So it is not admissible that an induced current is explained differently, depending on whether the magnet or the coil is in motion.

They are subject to various symmetry operations, like rotation or translation in space and time. The Special theory obeys the Lorentz-transformations, because the Galilean transformations fail as we approach the speed of light. The Galilean transformations, for instance, result in different values for the speed of light, if we change from a stationary to a moving reference frame.

The Lorentz-transformations deal with space-time transformations of a global kind; that is, they are constant throughout the space-time region. They form a symmetry group. The General theory requires a larger symmetry group. Symmetry constraints emphasize physical aspects: the symmetry operations return some values of parameters as invariant like the space-time interval and leave others as variant like the clock readings in different reference frames, in constant motion with respect to each other.

Symmetries result from transformations that leave all relevant structure intact. We are familiar with such symmetry transformations in daily life. We easily change the clock as we travel between different time zones.

But the tennis games we play at home and abroad are the same as far as the physical parameters are concerned. The modern use is quite different from the way Einstein uses the notion of covariance. Einstein associates covariance with the transformation rules of the theory of relativity. This leads to the characterization of covariance as form invariance. For Einstein a fit must exist between the theory of relativity and the material world.

We explicated fit in terms of the satisfaction of constraints, associated with the theory of relativity. If their amount and their interconnections can be increased, then many scientific theories will fail to satisfy the constraints. It will usually leave us with only one plausible survivor. For instance, after the development of the Special theory, Einstein increased the constraints on an admissible relativity theory.

Inertial reference frames should not be privileged over non-inertial frames.

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